The invention relates to a symbol code reader, comprising a two-dimensional array of photosensitive elements for converting light scattered by the symbol code into image signals representative of the symbol code, and image storage means for storing image signals produced by the photosensitive elements. Such a symbol code reader is generally known.
In symbol code readers, both two-dimensional arrays of photosensitive elements, such as area CCD-arrays, as well as one-dimensional arrays, such as linear CCD-arrays, can be used. Both types of arrays have specific advantages and disadvantages. Which type of array is used often depends on the type of code which is to be read. Many symbol codes, e.g. bar codes, have a linear structure. The Universal Product Code (UPC) for instance consists of a number of parallel bars extending perpendicularly to the general axis of the code. Because of this linear structure, it is possible to read such a code using a single row, i.e. a linear array, of photosensitive elements. However, in order to be able to read the code properly, it is necessary that the axis of the code is approximately aligned with the array. This alignment can be achieved by either moving the reader and the code into an approximately parallel mutual position, or by using image rotation means for optically rotating the image of the symbol code relative to the array.
Symbol code readers having a two-dimensional array of photosensitive elements have the advantage of being comparatively insensitive to the orientation of the symbol code relative to the array. There is no need to rotate the code in order to achieve alignment with the array, since the code can be read under almost any angle. Two-dimensional arrays however have the disadvantage of producing a multiple of the output signals (image signals) produced by a linear array. Whereas a linear CCD-array may contain 1000 photosensitive elements, an area CCD-array having the same resolution contains 100033 1000=1000000 elements. As each photosensitive element produces an image signal, a total of 106 image signals are outputted by the array. In order to deal with such a large number of image signals, a symbol code reader having a two-dimensional array of photosensitive elements should include relatively complex signal processing equipment. Considering the number of signals to be processed, the total processing time must necessarily be long.
It is therefore an object of the present invention to provide a symbol code reader having a two-dimensional array in which the number of image signals to be processed is greatly reduced.
It is a further object of the present invention to provide a symbol code reader having a two-dimensional array which produces no more image signals when reading one-dimensional codes than a reader having a one-dimensional array.
It is still a further object of the present invention to provide a symbol code reader which is virtually independent of the orientation of the symbol code relative to the reader and yet requires relatively simple signal processing means and short processing time.